1.2 - Physical & Chemical Changes & Properties of Matter

Qualitative Changes

Changes that describe qualities or characteristics of a substance without numerical values. Examples include color change, odor, or texture.

Quantitative Changes

Changes that involve numerical measurements and observations. Examples include changes in temperature, mass, volume, or length.

Significant Figures

The digits in a measured or calculated number that contribute to its precision. They include all known digits plus one estimated digit.

Volume

The amount of three-dimensional space an object or substance occupies. Common units include L, mL, and cm³

Density

A physical property of matter defined as the mass per unit volume of a substance, indicating how compactly mass is packed into a given space.

Density =

mass/volume

Volume =

mass/density

Why do substances have different densities?

The closer the atoms or molecules are packed together (i.e., less empty space), the denser the substance is. For example, solids are usually denser than liquids, which are much denser than gases.

Temperature

A measure of how hot or cold something is relative to some standard. We measure temperature with a thermometer.

Boiling Point

The temperature at which the liquid form of a substance changes to the gaseous form.

Melting Point

The substance changes from a solid to a liquid

Kelvin Scale

There are no negative values on the Kelvin scale. It is an absolute temperature scale because its zero point is the lowest possible temperature observable in the universe.

Absolute Temperature Scale

It is the Kelvin scale, and its unit symbol is K (it does not use the degree symbol ∘)

Fahrenheit, Celsius, & Kelvin Conversions

K=∘C+273.15

∘F=(∘C×59​)+32

Physical Change

A process that changes the physical properties of a substance without changing its chemical composition.

Boiling/Vaporization

The process where a substance changes from the liquid phase to the gas phase (vapor). It includes both evaporation and boiling.

Chemical Change

A process in which one or more substances are converted into one or more new substances.

Chemical Properties

Defined by what it is composed of and what chemical changes it can undergo. For example, let’s compare hydrogen and helium. Although they have similar physical properties (colorless gases, similar densities), their chemical properties are very different.

Chemical Reaction

A process that involves the rearrangement of the molecular or ionic structure of a substance, leading to the formation of one or more new substances.